1. Field of the Invention
The present invention generally relates to the field of carbon fiber production. More specifically, the invention relates to carbon fibers of micron, sub-micron, and nanometer size diameters.
2. Description of the Relevant Art
Fibers having small diameters (e.g., micrometer (“micron”) to nanometer (“nano”)) are useful in a variety of fields from the clothing industry to military applications. For example, in the biomedical field, there is a strong interest in developing structures based on nanofibers that provide a scaffolding for tissue growth to effectively support living cells. In the textile field, there is a strong interest in nanofibers because the nanofibers have a high surface area per unit mass that provide light, but highly wear resistant, garments. As a class, carbon nanofibers are being used, for example, in reinforced composites, in heat management, and in reinforcement of elastomers. Many potential applications for small-diameter fibers are being developed as the ability to manufacture and control their chemical and physical properties improves.
Specifically, carbon fibers (micro, sub micron and nanofibers) have been highly attractive mainly because of their structural performance, though fine carbon fibers also possess attractive applications, for example, as nonwoven cloths for: (1) filtration media where high temperature and corrosive environments are present; (2) filtration media such as activated carbon where the increase in surface area and small porosity enhances the performance; (3) filtration of odors such as in ostomy bags and HEPA filters; (4) energy storage; (5) batteries (anodes), textiles to be used to shield electronics (EMI/RF protection); (5) high temperature fire retardant insulation; (6) nonwoven cloths to be used as prepregs to add strength to composite materials; (7) gas diffusion electrodes and fuel cell electrodes; (8) protective clothing; and (9) thermal and acoustical insulation (aircrafts, automotive) to mention some.
Most small-diameter carbon fibers are made using carbonization methods where high temperatures are used to produce carbon fibers from polymeric materials (e.g., polyacrylonitrile (PAN)). In the case of nanofibers or nanotubes, other processes exist that are mainly dependent on the use of catalysts (e.g., transition metals such as cobalt, nickel or iron) where the carbon fibers are grown through the attachment of carbon atoms flowing in the reactor (e.g., from methane gas). Recently, carbon fibers were produced by carbonization of polyethylene fibers with assistance of a sulfonation process.
Most methods used to prepare carbon fibers are expensive and/or time consuming. It is desirable to have a method of preparing carbon fibers specifically nonwoven carbon cloths from low cost starting materials without the need for high temperatures or transition metal catalysts.
While the invention may be susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. The drawings may not be to scale. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but to the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.